One of the more recent technological innovations has been the utilization of microfilm to store the information generated by computers. The computer provides a visual output, for example, on a screen of a cathode ray tube which output is then photographed onto microfilm. To achieve full utilization of information stored on microfilm, it is desirable to print such variable information onto forms having preprinted information thereon. The preprinted forms may comprise business operations letterhead, distinctive logo, or other similar type of non-varying information on a continuous strip or web. It is necessary, therefore, to transfer or print the variable prerecorded information from the microfilm onto the web so that the variable information is accurately registered with the preprinted information with a minimum of distortion. The availability of commercial machines for printing the variable information on microfilm in registration with preprinted information has been extremely limited.
Recently it has been proposed that a xerographic copying machine be employed to directly utilize microfilm having variable data photographed thereon, the microfilm having the variable data functioning as the original document for copying purposes. A copy medium, preferably a web of paper, would have preprinted, non-variable information provided thereon.
In the type of system described it is desirable to have a system for projecting the images from the microfilm at various desired magnification ratios with a minimum of distortion onto the preprinted web. In the prior art xerographic systems, copying of microfilm has customarily been accomplished by the use of fixed focal length lenses. The change the magnification, it was necessary to change the track length (the overall optical distance from the object to image) and then refocus the lens systems. Alternatively, the prior art provided "add" lenses which were added to the original lens system to extend the useful range of magnification. Magnification would be changed in the former, by moving the film gate or the image receptor, i.e., xerographic plate or drum, with their associated mechanisms, or, in the latter situation, by inserting add lens and then refocusing the system. The complexities and inaccuracies with these techniques are quite obvious.
The convenience of a mechanically conpensated zoom lens system which avoids the deficiences noted hereinabove is disclosed, for example, in U.S. Pat. Nos. 3,360,325 and 3,640,605 which describe prior art systems for solving this problem. Although adequate for the purposes envisioned in the aforementioned patents, the disclosed systems do not meet the necessary resolution and distortion requirements in the required spectral band and magnification ranges as in the projection system described hereinabove.